Capacitive coupling plasma processing apparatus and method

ABSTRACT

A plasma processing apparatus includes a process container configured to accommodate a target substrate and to be vacuum-exhausted. A first electrode and a second electrode are disposed opposite each other within the process container. A process gas supply unit is configured to supply a process gas into the process container. An RF power supply is configured to apply an RF power to the first electrode or second electrode to generate plasma of the process gas. A DC power supply is configured to apply a DC voltage to the first electrode or second electrode. A control section is configured to control the RF power supply and the DC power supply such that the DC power supply causes the DC voltage applied therefrom to reach a voltage set value, when or after the RF power supply starts applying the RF power.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/666,696, filed Mar. 31, 2005.

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2005-102952, filed Mar. 31, 2005,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a plasma processing apparatus andmethod of the capacitive coupling type, used for performing a plasmaprocess on a target substrate in, e.g., a semiconductor processingsystem. The term “semiconductor process” used herein includes variouskinds of processes which are performed to manufacture a semiconductordevice or a structure having wiring layers, electrodes, and the like tobe connected to a semiconductor device, on a target substrate, such as asemiconductor wafer or a glass substrate used for an LCD (Liquid CrystalDisplay) or FPD (Flat Panel Display), by forming semiconductor layers,insulating layers, and conductive layers in predetermined patterns onthe target substrate.

2. Description of the Related Art

In the process of manufacturing semiconductor devices, plasma etchingprocesses are often used to form circuits on a semiconductor wafertreated as a target substrate. There are various plasma etchingapparatuses for performing such plasma etching, but parallel-plateplasma processing apparatuses of the capacitive coupling type arepresently in the mainstream.

In general, a parallel-plate plasma etching apparatus of the capacitivecoupling type includes a chamber with parallel-plate electrodes (upperand lower electrodes) disposed therein. While a process gas is suppliedinto the chamber, an RF (radio frequency) is applied to one of theelectrodes to form an RF electric field between the electrodes. Theprocess gas is ionized into plasma by the RF electric field, therebyperforming a plasma etching process on a semiconductor wafer.

In recent years, design rules for ULSIs have been increasinglyminiaturized, and the shape of holes is required to have a higher aspectratio. For this reason, there is a proposal to use an application RFpower with a higher frequency, so as to generate high density plasmawhile maintaining a good dissociation state of the plasma. This methodmakes it possible to suitably generate plasma under a lower pressure,which can meet miniaturization of design rules.

However, even where such an RF power with a higher frequency is used,plasma uniformity is still unsatisfactory. In order to solve thisproblem, Jpn. Pat. Appln. KOKAI Publication No. 2000-323460 (PatentDocument 1) discloses a plasma processing technique. According to thistechnique, an upper electrode is supplied with a DC (direct current)voltage, as well ask an RF power with a frequency of 27 MHz or more, tocontrol plasma so as to uniformize the plasma density.

Where a DC voltage is applied as in the technique disclosed in PatentDocument 1, the application timing of the DC voltage should beinfluential on plasma generation. However, Patent Document 1 is silentabout the application timing of the DC voltage to generate stable andgood plasma.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to generate good plasma in aplasma processing apparatus and method of the capacitive coupling typein which a DC voltage is applied in addition to an RF power.

According to a first aspect of the present invention, there is provideda plasma processing apparatus comprising:

a process container configured to accommodate a target substrate and tobe vacuum-exhausted;

a first electrode and a second electrode disposed opposite each otherwithin the process container;

a process gas supply unit configured to supply a process gas into theprocess container;

an RF power supply configured to apply an RF power to the firstelectrode or second electrode to generate plasma of the process gas;

a DC power supply configured to apply a DC voltage to the firstelectrode or second electrode; and

a control section configured to control the RF power supply and the DCpower supply,

wherein the control section performs control such that the DC powersupply causes the DC voltage applied therefrom to reach a voltage setvalue, when or after the RF power supply starts applying the RF power.

According to a second aspect of the present invention, there is provideda plasma processing apparatus comprising:

a process container configured to accommodate a target substrate and tobe vacuum-exhausted;

a first electrode disposed within the process container and configuredto serve as an upper electrode;

a second electrode disposed opposite the first electrode within theprocess container and configured to serve as a lower electrode to placethe target substrate thereon;

a process gas supply unit configured to supply a process gas into theprocess container;

a first RF power supply configured to apply a first RF power to thefirst electrode to generate plasma of the process gas;

a second RF power supply configured to apply a second RF power to thesecond electrode to attract ions toward the target substrate;

a DC power supply configured to apply a DC voltage to the firstelectrode; and

a control section configured to control the first and second RF powersupplies and the DC power supply,

wherein the control section performs control such that the DC powersupply causes the DC voltage applied therefrom to reach a voltage setvalue, when or after the first RF power supply starts applying the firstRF power.

According to a third aspect of the present invention, there is provideda plasma processing method for performing a plasma process on a targetsubstrate in a plasma processing apparatus,

the plasma processing apparatus comprising

a process container configured to accommodate a target substrate and tobe vacuum-exhausted,

a first electrode and a second electrode disposed opposite each otherwithin the process container,

a process gas supply unit configured to supply a process gas into theprocess container,

an RF power supply configured to apply an RF power to the firstelectrode or second electrode to generate plasma of the process gas, and

a DC power supply configured to apply a DC voltage to the firstelectrode or second electrode, and

the plasma processing method comprising:

performing control such that the DC power supply causes the DC voltageapplied therefrom to reach a voltage set value, when or after the RFpower supply starts applying the RF power.

According to a fourth aspect of the present invention, there is provideda plasma processing method for performing a plasma process on a targetsubstrate in a plasma processing apparatus,

the plasma processing apparatus comprising

a process container configured to accommodate a target substrate and tobe vacuum-exhausted,

a first electrode disposed within the process container and configuredto serve as an upper electrode,

a second electrode disposed opposite the first electrode within theprocess container and configured to serve as a lower electrode to placethe target substrate thereon,

a process gas supply unit configured to supply a process gas into theprocess container,

a first RF power supply configured to apply a first RF power to thefirst electrode to generate plasma of the process gas,

a second RF power supply configured to apply a second RF power to thesecond electrode to attract ions toward the target substrate, and

a DC power supply configured to apply a DC voltage to the firstelectrode,

the plasma processing method comprising:

performing control such that the DC power supply causes the DC voltageapplied therefrom to reach a voltage set value, when or after the firstRF power supply starts applying the first RF power.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention, andtogether with the general description given above and the detaileddescription of the embodiments given below, serve to explain theprinciples of the invention.

FIG. 1 is a sectional view schematically showing a plasma etchingapparatus according to an embodiment of the present invention;

FIG. 2 is a view showing a matching unit connected to a first RF (radiofrequency) power supply in the plasma etching apparatus shown in FIG. 1;

FIG. 3 is a view showing a preferable example of an applicationsequence, which involves the DC (direct current) voltage of a variableDC power supply and the RF powers of first and second RF power supplies,along with the ON/OFF of a relay circuit, used in the plasma etchingapparatus shown in FIG. 1;

FIG. 4 is a view showing another preferable example of an applicationsequence, which involves the DC voltage of the variable DC power supplyand the RF powers of the first and second RF power supplies, along withthe ON/OFF of the relay circuit, used in the plasma etching apparatusshown in FIG. 1;

FIG. 5 is a view showing a preferable example of an applicationsequence, which involves the DC voltage of the variable DC power supplyand the RF powers of the first and second RF power supplies, along withthe ON/OFF of the relay circuit, used for ending plasma etching in theplasma etching apparatus shown in FIG. 1;

FIG. 6 is a view showing another preferable example of an applicationsequence, which involves the DC voltage of the variable DC power supplyand the RF powers of the first and second RF power supplies, along withthe ON/OFF of the relay circuit, used for ending plasma etching in theplasma etching apparatus shown in FIG. 1;

FIG. 7 is a view showing an alternative preferable example of anapplication sequence, which involves the DC voltage of the variable DCpower supply and the RF powers of the first and second RF powersupplies, along with the ON/OFF of the relay circuit, used in the plasmaetching apparatus shown in FIG. 1;

FIG. 8 is a view showing a further alternative preferable example of anapplication sequence, which involves the DC voltage of the variable DCpower supply and the RF powers of the first and second RF powersupplies, along with the ON/OFF of the relay circuit, used in the plasmaetching apparatus shown in FIG. 1;

FIG. 9 is a view showing a further alternative preferable example of anapplication sequence, which involves the DC voltage of the variable DCpower supply and the RF powers of the first and second RF powersupplies, along with the ON/OFF of the relay circuit, used in the plasmaetching apparatus shown in FIG. 1;

FIG. 10 is a view showing change in V_(dc) (a DC voltage generated inthe upper electrode) and plasma sheath thickness where a DC voltage isapplied to the upper electrode in the plasma etching apparatus shown inFIG. 1;

FIGS. 11A and 11B are views showing plasma states in comparison where aDC voltage is applied and where no DC voltage is applied, in the plasmaetching apparatus shown in FIG. 1;

FIG. 12 is a view schematically showing a plasma etching apparatus of analternative type according to another embodiment of the presentinvention;

FIG. 13 is a view schematically showing a plasma etching apparatus ofthe alternative type according to another embodiment of the presentinvention;

FIG. 14 is a view schematically showing a plasma etching apparatus of afurther alternative type according to another embodiment of the presentinvention; and

FIG. 15 is a view schematically showing a plasma etching apparatus ofthe further alternative type according to another embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will now be described withreference to the accompanying drawings. In the following description,the constituent elements having substantially the same function andarrangement are denoted by the same reference numerals, and a repetitivedescription will be made only when necessary.

FIG. 1 is a sectional view schematically showing a plasma etchingapparatus according to an embodiment of the present invention. Thisplasma etching apparatus is structured as a parallel-plate plasmaetching apparatus of the capacitive coupling type. The apparatusincludes a cylindrical chamber (process container) 10, which is made of,e.g., aluminum with an anodization-processed surface. The chamber 10 isprotectively grounded.

A columnar susceptor pedestal 14 is disposed on the bottom of thechamber 10 through an insulating plate 12 made of, e.g., a ceramic. Asusceptor 16 made of, e.g., aluminum is disposed on the susceptorpedestal 14. The susceptor 16 is used as a lower electrode, on which atarget substrate, such as a semiconductor wafer W, is placed.

The susceptor 16 is provided with an electrostatic chuck 18 on the top,for holding the target substrate or semiconductor wafer W by anelectrostatic attraction force. The electrostatic chuck 18 comprises anelectrode 20 made of a conductive film, and a pair of insulating layersor insulating sheets sandwiching the electrode 20. The electrode 20 iselectrically connected to a DC (direct current) power supply 22, and theconnection thereof is turned on and off by an ON/OFF switch 22 a. Thesemiconductor wafer W is attracted and held on the electrostatic chuck18 by an electrostatic attraction force, e.g., a Coulomb force,generated by a DC voltage applied from the DC power supply 22. TheON/OFF operation of the ON/OFF switch 22 a is controlled by a controller23.

A conductive focus ring (correction ring) 24 made of, e.g., silicon isdisposed on the top of the susceptor 16 to surround the electrostaticchuck 18 (and the semiconductor wafer W) to improve etching uniformity.A cylindrical inner wall member 26 made of, e.g., quartz is attached tothe side of the susceptor 16 and susceptor pedestal 14.

The susceptor pedestal 14 is provided with a cooling medium space 28formed therein. A cooling medium set at a predetermined temperature,such as cooling water, is circulated within the cooling medium space 28from an external chiller unit (not shown) through lines 30 a and 30 b.The temperature of the cooling medium is set to control the processtemperature of the semiconductor wafer W placed on the susceptor 16.Further, a heat transmission gas, such as He gas, is supplied from aheat transmission gas supply unit (not shown), through a gas supply line32, into the interstice between the top surface of the electrostaticchuck 18 and the bottom surface of the semiconductor wafer W.

An upper electrode 34 is disposed above the lower electrode or susceptor16 in parallel with the susceptor. The space between the electrodes 16and 34 is used as a plasma generation space. The upper electrode 34defines a surface facing the semiconductor wafer W placed on the lowerelectrode or susceptor 16, and thus this facing surface is in contactwith the plasma generation space.

The upper electrode 34 is supported at the top of the chamber 10 by aninsulating shield member 42. The upper electrode 34 includes anelectrode plate 36 defining the facing surface opposite the susceptor 16and having a number of gas delivery holes 37, and an electrode support38 detachably supporting the electrode plate 36. The electrode support38 is made of a conductive material, such as aluminum with ananodization-processed surface, and has a water-cooled structure. Theelectrode plate 36 is preferably made of a conductor or semiconductorhaving a low resistivity and thus generating less Joule heat. Further,in order to reinforce a resist film, as described later, the electrodeplate 36 is preferably made of a silicon-containing substance. In lightof these factors, the electrode plate 36 is preferably made of siliconor SiC. The electrode support 38 has a gas diffusion cell 40 formedtherein, which is connected to the gas delivery holes 37 through anumber of gas flow channels 41 extending downward.

Further, the electrode support 38 has a gas feed port 62 formed thereinfor feeding a process gas into the gas diffusion cell 40. The gas feedport 62 is connected to a process gas supply source 66 through a gassupply line 64. The gas supply line 64 is provided with a mass-flowcontroller (MFC) 68 and a switching valve 70 disposed thereon in thisorder from the upstream. A process gas for etching, such as afluorocarbon gas (C_(x)F_(y)), e.g., C₄F₈ gas, is supplied from theprocess gas supply source 66 through the gas supply line 64 into the gasdiffusion cell 40. Then, the process gas flows through the gas flowchannels 41 and is delivered from the gas delivery holes 37 into theplasma generation space, as in a shower device. In other words, theupper electrode 34 serves as a showerhead for supplying a process gas.

The upper electrode 34 is electrically connected to a first RF powersupply 48 through a matching unit 46 and a feed rod 44. The first RFpower supply 48 outputs an RF power with a frequency of 13.56 MHz ormore, such as 60 MHz. The matching unit 46 is arranged to match the loadimpedance with the internal (or output) impedance of the first RF powersupply 48. When plasma is generated within the chamber 10, the matchingunit 46 performs control for the output impedance of the first RF powersupply 48 to apparently agree with the load impedance. The outputterminal of the matching unit 46 is connected to the top of the feed rod44. The ON/OFF operation and power of the first RF power supply 48 arecontrolled by a controller 49.

Further, the upper electrode 34 is electrically connected to a variableDC power supply 50 in addition to the first RF power supply 48. Thevariable DC power supply 50 is preferably formed of a bipolar powersupply. Specifically, the variable DC power supply 50 is connected tothe upper electrode 34 through the matching unit 46 and feed rod 44, andthe connection thereof is turned on and off by a relay circuit (ON/OFFswitch) 52. The polarity, current, and voltage of the variable DC powersupply 50 and the ON/OFF operation of the relay circuit 52 arecontrolled by a controller 51.

FIG. 2 is a view showing the matching unit 46 connected to the first RFpower supply 48 in the plasma etching apparatus shown in FIG. 1. Asshown in FIG. 2, the matching unit 46 includes a first variablecapacitor 54 branched from a feed line 49 of the first RF power supply48, and a second variable capacitor 56 disposed on the feed line 49downstream from the branch point, so as to exercise the functiondescribed above. The matching unit 46 also includes a filter 58configured to trap the RF power (for example, 60 MHz) from the first RFpower supply 48 and the RF power (for example, 2 MHz) from a second RFpower supply described later, so that a DC voltage current (which willbe simply referred to as a DC voltage) is effectively supplied to theupper electrode 34. As a consequence, a DC current is connected from thevariable DC power supply 50 through the filter 58 to the feed line 49.The filter 58 is formed of a coil 59 and a capacitor 60 arranged to trapthe RF power from the first RF power supply 48 and the RF power from thesecond RF power supply described later.

The sidewall of the chamber 10 extends upward above the height level ofthe upper electrode 34 and forms a cylindrical grounded conductive body10 a. The top wall of the cylindrical grounded conductive body 10 a iselectrically insulated from the upper feed rod 44 by a tube-likeinsulating member 44 a.

The susceptor 16 used as a lower electrode is electrically connected toa second RF power supply 90 through a matching unit 88. The RF powersupplied from the second RF power supply 90 to the lower electrode orsusceptor 16 is used for attracting ions toward the semiconductor waferW. The second RF power supply 90 outputs an RF power with a frequency of2 to 27 MHz, such as 2 MHz. The matching unit 88 is arranged to matchthe load impedance with the internal (or output) impedance of the secondRF power supply 90. When plasma is generated within the chamber 10, thematching unit 88 performs control for the internal impedance of thesecond RF power supply 90 to apparently agree with the load impedance.The ON/OFF operation and power of the second RF power supply 90 arecontrolled by a controller 91.

The upper electrode 34 is electrically connected to a low-pass filter(LPF) 92, which prevents the RF (60 MHz) from the first RF power supply48 from passing through, while it allows the RF (2 MHz) from the secondRF power supply 98 to pass through to ground. The low-pass filter (LPF)92 is preferably formed of an LR filter or LC filter. However, a singleconducting wire can apply a sufficiently large reactance to the RF power(60 MHz) from the first RF power supply 48, and thus such a wire may beused in place of the LPF 92. On the other hand, the lower electrode orsusceptor 16 is electrically connected to a high-pass filter (HPF) 94,which allows the RF (60 MHz) from the first RF power supply 48 to passthrough to ground.

An exhaust port 80 is formed at the bottom of the chamber 10, and isconnected to an exhaust unit 84 through an exhaust line 82. The exhaustunit 84 includes a vacuum pump, such as a turbo molecular pump, toreduce the pressure inside the chamber 10 to a predetermined vacuumlevel. A transfer port 85 for a semiconductor wafer W is formed in thesidewall of the chamber 10, and is opened/closed by a gate valve 86attached thereon. A deposition shield 11 is detachably disposed alongthe inner wall of the chamber 10 to prevent etching by-products(deposition) from being deposited on the wall. In other words, thedeposition shield 11 constitutes a chamber wall. A deposition shield 11is also disposed around the inner wall member 26. An exhaust plate 83 isdisposed at the bottom of the chamber 10 between the deposition shield11 on the chamber wall and the deposition shield 11 on the inner wallmember 26. The deposition shield 11 and exhaust plate 83 are preferablymade of an aluminum body covered with a ceramic, such as Y₂O₃.

A conductive member (GND block) 87 is disposed on a portion of thedeposition shield 11 that constitutes the chamber inner wall, at aheight essentially the same as the wafer W, and is connected to groundin the sense of DC. The GND block 87 is exposed to plasma, and iselectrically connected to a conductive portion in the deposition shield11. The DC voltage current applied from the variable DC power supply 50to the upper electrode 34 flows through the process space to the GNDblock 87, and is then grounded through the deposition shield 11. The GNDblock 87 allows electrons accumulated in the upper electrode 34 to bereleased, thereby preventing abnormal electric discharge. The GND block87 is made of a conductor, and preferably a silicon-containingsubstance, such as Si or SiC. The GND block 87 may be preferably made ofC.

The position of the GND block 87 is not limited to that shown in FIG. 1,as long as it is disposed in the plasma generation area. For example,the GND block 87 may be disposed on the susceptor 16 side, e.g., aroundthe susceptor 16. Alternatively, the GND block 87 may be disposed nearthe upper electrode 34, e.g., as a ring disposed outside the upperelectrode 34.

Respective portions of the plasma etching apparatus are connected to andcontrolled by a control section (process controller) 95. In thisembodiment, the ON/OFF operation and power of the first RF power supply48 are controlled by a controller 49. The ON/OFF operation and power ofthe second RF power supply 90 are controlled by a controller 91. Thepolarity, current, and voltage of the variable DC power supply 50 andthe ON/OFF operation of the relay circuit 52 are controlled by acontroller 51. The ON/OFF operation of the ON/OFF switch 22 a forswitching the DC power supply 22 is controlled by a controller 23. Thesecontrollers 49, 91, 51, and 23 are operated by the control section 95 tocontrol the timing of performing and stopping applications of the powersand voltage described above.

The control section 95 is connected to a user interface 96 including,e.g., a keyboard and a display, wherein the keyboard is used for aprocess operator to input commands for operating the plasma etchingapparatus, and the display is used for showing visualized images of theoperational status of the plasma processing apparatus.

Further, the control section 95 is connected to a storage section 97that stores control programs for the control section 95 to control theplasma etching apparatus so as to perform various processes, andprograms or recipes for respective components of the plasma etchingapparatus to perform processes in accordance with process conditions.Recipes may be stored in a hard disk or semiconductor memory, or storedin a computer readable portable storage medium, such as a CDROM or DVD,to be attached to a predetermined position in the storage section 97.

A required recipe is retrieved from the storage section 97 and executedby the control section 95 in accordance with an instruction or the likethrough the user interface 96. As a consequence, the plasma etchingapparatus can perform a predetermined process under the control of thecontrol section 95.

When an etching process is performed in the plasma etching apparatusdescribed above, the gate valve 86 is first opened, and a semiconductorwafer W to be etched is transferred into the chamber 10 and placed onthe susceptor 16. Then, a process gas for etching is supplied from theprocess gas supply source 66 into the gas diffusion cell 40 at apredetermined flow rate, and then supplied into the chamber 10 throughthe gas flow channels 41 and gas delivery holes 37. At the same time,the interior of the chamber 10 is exhausted by the exhaust unit 84 toset the pressure inside the chamber 10 to be a predetermined valuewithin a range of, e.g., 0.1 to 150 Pa. The process gas may be selectedfrom various gases conventionally employed, and preferably is a gascontaining a halogen element, a representative of which is afluorocarbon gas (C_(x)F_(y)), such as C₄F₈ gas. Further, the processgas may contain another gas, such as Ar gas or O₂ gas.

While the etching gas is supplied into the chamber 10, an RF power forplasma generation is applied from the first RF power supply 48 to theupper electrode 34 at a predetermined power level. At the same time, anRF power for ion attraction is applied from the second RF power supply90 to the lower electrode or susceptor 16 at a predetermined powerlevel. Further, a predetermined DC voltage is applied from the variableDC power supply 50 to upper electrode 34.

At this time, the controllers 49, 51, and 91 are operated by the controlsection 95 to control the timing of performing applications of thepowers and voltage described above. Specifically, control is performedsuch that the variable DC power supply 50 causes the DC voltage appliedtherefrom to reach a voltage set value prescribed in a recipe, when orafter the first RF power supply 48 starts applying the RF power. Setvalues used hereinafter denote the values of the DC voltage or RF powersused to perform the etching process.

This control is adopted to prevent abnormal electric discharge fromoccurring, which can be achieved by causing the application DC voltagenot to reach the voltage set value until the first RF power supply 48starts applying the RF power for the first time to thereby ignite theplasma. If the DC voltage applied reaches its set value while no plasmais present within the chamber 10, abnormal electric discharge can easilyoccur, even though this results in little damage to the wafer W.Preferably, the variable DC power supply 50 starts applying the DCvoltage after the first RF power supply 48 starts applying the RF power.Where the DC voltage starts being applied after the first RF powersupply 48 starts applying the RF power to thereby ignite the plasma, itis possible not only to prevent abnormal electric discharge, but also toperform the voltage application smoothly. Further, preferably, the DCvoltage starts being applied after the RF power applied from the firstRF power supply 48 reaches its set value. This makes it possible to morereliably prevent abnormal electric discharge from occurring.

Next, with reference to FIG. 3, an explanation will be given of apreferable example of an application sequence involving the RF power ofthe second RF power supply 90, as well as the DC voltage of the variableDC power supply 50 and the RF power of the first RF power supply 48.FIG. 3 is a view showing a preferable example of an applicationsequence, which involves the DC voltage of the variable DC power supply50 and the RF powers of first and second RF power supplies 48 and 90,along with the ON/OFF of the relay circuit 52, used in the plasmaetching apparatus shown in FIG. 1.

At first, the second RF power supply 90 starts applying an RF power,such as 300 W, lower than its set value, to the lower electrode orsusceptor 16. Then, when 0.1 to 2.4 seconds, such as 0.5 seconds, haveelapsed, the first RF power supply 48 starts applying an RF power at itsset value, such as 2,400 W, to the upper electrode 34. Then, forexample, when 2.0 seconds have elapsed, the second RF power supply 90shifts the application power to its set value, such as 3,800 W. Prior tothis (for example, when 2.3 seconds have elapsed since the second RFpower supply 90 started applying the RF power), the variable DC powersupply 50 starts applying a DC voltage at its set value, such as −900V,to the upper electrode 34. If the DC voltage starts being applied afterthe second RF power supply 90 shifts the application power to its setvalue, the plasma may cause hunching. As described above, the second RFpower supply 90 first applies an RF power lower than its set value, andthen shifts the RF power to its set value (full power) after matching ofthe first RF power supply 48 is obtained (for example, when 1.5 secondshave elapsed since the first RF power supply started applying the RFpower).

Further, before the DC voltage starts being applied and preferablybefore the first and second RF power supplies 48 and 90 start applyingthe RF powers, the relay circuit 52 is turned on to be ready for the DCvoltage application. However, it is not preferable to always set therelay circuit 52 in an ON-state, and thus the relay circuit 52 shouldonly be turned on, when needed.

The timing at which the DC voltage reaches its set value may be made tocoincide with the time point at which the first RF power supply 48starts applying the RF power, instead of after the first RF power supply48 starts applying the RF power. FIG. 4 is a view showing anotherpreferable example of an application sequence, which involves the DCvoltage of the variable DC power supply 50 and the RF powers of firstand second RF power supplies 48 and 90, along with the ON/OFF of therelay circuit 52, used in the plasma etching apparatus shown in FIG. 1.

At first, before the first and second RF power supplies 48 and 90 startapplying RF powers, the relay circuit 52 is turned on to be ready forthe DC voltage application. Then, as in the case shown in FIG. 3, thesecond RF power supply 90 starts applying an RF power lower than its setvalue to the susceptor 16. Then, the first RF power supply 48 startsapplying an RF power at its set value to the upper electrode 34. At thesame time the first RF power supply 48 starts applying the RF power, thevariable DC power supply 50 starts applying a DC voltage at its setvalue to the upper electrode 34. Then, the second RF power supply 90shifts the application power to its set value. With this arrangement, itis possible to prevent abnormal electric discharge from occurring, as inthe case described above where the DC voltage reaches its set valueafter the first RF power supply 48 starts applying the RF power. Inother words, the timing for the DC voltage to reach its set value may beplaced at any time point, as long as it is not before the first RF powersupply 48 starts applying the RF power.

Further, in accordance with an instruction from the control section 95,the controller 23 operates the ON/OFF switch 22 a to turn on the DCpower supply 22 at a predetermined timing. Consequently, a DC voltage isapplied to the electrode 20 of the electrostatic chuck 18 to fix thesemiconductor wafer W on the susceptor 16. The timing for the DC powersupply 22 to apply the DC voltage is not limited to a specific one, andmay be placed after the first RF power supply 48 starts applying the RFpower and the variable DC power supply 50 starts applying the DCvoltage.

The process gas delivered from the gas delivery holes 37 formed in theelectrode plate 36 of the upper electrode 34 is ionized into plasma byglow discharge caused by the RF power applied across the upper electrode34 and the lower electrode or susceptor 16. Radicals and ions generatedin this plasma are used to etch the target surface of the semiconductorwafer W.

In this plasma etching apparatus, the upper electrode 34 is suppliedwith an RF power with a frequency selected from a high frequency range(such as 10 MHz or more, which ions cannot follow). In this case, sincethe density of plasma can be higher with a preferable dissociationstate, high density plasma can be generated even under a low pressure.

When the plasma is generated, the variable DC power supply 50 applies aDC voltage with a predetermined polarity and value to the upperelectrode 34 at the timing described above. Consequently, stable andgood plasma is generated without increasing damage to the wafer W, so asto provide effects described later.

As shown in FIG. 1, the voltage applied from the variable DC powersupply 50 to the upper electrode 34 is preferably set to be a negativevoltage. A positive voltage may be used, but it makes the plasmaunstable. Accordingly, where a positive voltage is applied, it isrequired to prepare some countermeasures, such as pulse-wiseapplication.

After the predetermined etching process is finished, the first andsecond RF power supplies 48 and 90 and the variable DC power supply 50are turned off to extinguish plasma. Preferable examples of a sequenceat this time will be explained with reference to FIGS. 5 and 6. FIGS. 5and 6 are views showing two different preferable examples of anapplication sequence, which involves the DC voltage of the variable DCpower supply 50 and the RF powers of first and second RF power supplies48 and 90, along with the ON/OFF of the relay circuit 52, used forending plasma etching in the plasma etching apparatus shown in FIG. 1.

The timing of extinguishing plasma is not limited to a specific one, butit is preferable to turn off the RF power application of the first andsecond RF power supplies 48 and 90 after turning off the DC voltageapplication of the variable DC power supply 50, as shown in FIG. 5.Further, it is more preferable to turn off the DC voltage application ofthe variable DC power supply 50, the RF power application of the firstRF power supply 48, and the RF power application of the second RF powersupply 90 at the same time, as shown in FIG. 6. In contrast, if turningoff the DC voltage application of the variable DC power supply 50 comesafter turning off the RF power application of the first and second RFpower supplies 48 and 90, the following problem arises. Specifically,after turning off the RF power application, the interior of the chamber10 comes into a vacuum state, which has a higher resistance, and thus anovershoot phenomenon may occur when a DC voltage current passestherethrough.

In order to protect the relay circuit 52, the relay circuit 52 is turnedoff after the variable DC power supply 50 stops applying the DC voltageand the first and second RF power supplies 48 and 90 stop applying theRF powers. Further, it is also important to select a plasma extinguishsequence that can prevent particle deposition on the wafer W, inaccordance with process conditions. In order to prevent particledeposition, it is also effective to apply a reverse polarity voltagebefore turning off the DC voltage from the variable DC power supply 50.

In an experiment, the sequence shown in FIG. 3 was performed. A resultof this experiment will be explained below.

The pressure inside a chamber was set at 3.3 Pa, and an etching gas ofC₄F₈/Ar/N₂ was supplied at a flow rate of 6/1,000/180 mL/min into thechamber. Power application was performed in accordance with the sequenceshown in FIG. 3, while the first RF power supply 48 output a power witha frequency of 60 MHz and a set value of 2,400 W, the second RF powersupply 90 output a power with a set value of 3,800 W, and the variableDC power supply 50 output a voltage with a set value of −900V. Underthese conditions, plasma was generated to perform etching on an oxidefilm on a wafer W.

Specifically, at first, the second RF power supply 90 started applyingan RF power, such as 300 W, lower than its set value, to the lowerelectrode or susceptor 16. Then, when 0.5 seconds had elapsed since thestart of the power application, the first RF power supply 48 startedapplying an RF power at the set value of 2,400 W to the upper electrode34. Then, when 2.0 seconds had elapsed, the second RF power supply 90shifted the application power to the set value of 3,800 W. Prior tothis, when 2.3 seconds had elapsed since the second RF power supply 90started applying the RF power, the variable DC power supply 50 startedapplying a DC voltage at the set value of −900V to the upper electrode34. As a result, stable and good plasma was generated. From this result,it has been confirmed that the application timing of the DC voltageaccording to this embodiment can generate stable and good plasma withoutcausing abnormal electric discharge.

Next, with reference to FIG. 7, an explanation will be given of anotherpreferable example of an application sequence involving the DC voltageof the variable DC power supply 50 and the RF powers of the first andsecond RF power supplies 48 and 90. FIG. 7 is a view showing analternative preferable example of an application sequence, whichinvolves the DC voltage of the variable DC power supply 50 and the RFpowers of first and second RF power supplies 48 and 90, along with theON/OFF of the relay circuit 52, used in the plasma etching apparatusshown in FIG. 1.

At first, as in the case shown in FIG. 3, the second RF power supply 90starts applying an RF power, such as 300 W, lower than its set value, tothe lower electrode or susceptor 16. Then, when 0.1 to 2.4 seconds, suchas 0.5 seconds, have elapsed, the first RF power supply 48 startsapplying an RF power at its set value to the upper electrode 34. At thesame time when the first RF power supply 48 starts applying the RF poweror thereafter, the variable DC power supply 50 starts applying a DCvoltage to the upper electrode 34 under control such that theapplication voltage is gradually increased to eventually reach its setvalue, such as −900V (i.e., gradual increase control). Then, forexample, when 2.0 seconds have elapsed since the first RF power supply48 started applying the RF power, the second RF power supply 90 shiftsthe application power to its set value. Where the DC voltage from thevariable DC power supply 50 is gradually increased, as described above,the feed circuit of the variable DC power supply 50 can be less forcedwhile damage to the wafer W is suppressed. The voltage boosting rate atthis time is not limited to a specific one, and this rate can besuitably adjusted to be, e.g., around 1 kV/second, in accordance with aset voltage.

Further, before the DC voltage starts being applied and preferablybefore the first and second RF power supplies 48 and 90 start applyingthe RF powers, the relay circuit 52 is turned on to be ready for the DCvoltage application.

In the example described above, the variable DC power supply 50 iscontrolled to gradually increase the application voltage. Alternatively,control may be performed such that the application current orapplication power is gradual increased to eventually reach its setvoltage. Further, where any one of the application voltage, applicationcurrent, and application power is gradually increased, an interlockfunction may be arranged. Specifically, where any one of theseparameters is gradually increased, the controller 51 may be providedwith a function to stop the power application when the absolute value orincreased portion of the parameter exceeds its set value. With thisarrangement, it is possible to more effectively prevent the variable DCpower supply 50 and the feed circuit thereof from suffering an overload.

In an experiment, the voltage was gradually increased in accordance thesequence shown in FIG. 7. A result of this experiment will be explainedbelow.

The pressure inside a chamber was set at 3.3 Pa, and an etching gas ofC₄F₈/Ar/O₂ was supplied at a flow rate of 30/1,000/20 mL/min into thechamber. Power application was performed in accordance with the sequenceshown in FIG. 7, while the first RF power supply 48 output a power witha frequency of 60 MHz and a set value of 1,800 W, the second RF powersupply 90 output a power with a set value of 3,800 W, and the variableDC power supply 50 output a voltage with a set value of −900V. Underthese conditions, plasma was generated to perform etching on an oxidefilm on a wafer W.

Specifically, at first, the second RF power supply 90 started applyingan RF power, such as 300 W, lower than its set value, to the lowerelectrode or susceptor 16. Then, when 0.5 seconds had elapsed since thestart of the power application, the first RF power supply 48 startedapplying an RF power at the set value of 1,800 W to the upper electrode34. At the same time, the variable DC power supply 50 started applying aDC voltage to the upper electrode 34, such that the application voltageis gradually increased to the set value of −900V in about 8.0 seconds.Then, when 2.0 seconds had elapsed since the first RF power supply 48started applying the RF power, the second RF power supply 90 shifted theapplication power to the set value of 3,800 W (experiment A). Forcomparison, when 2.3 seconds had elapsed since the second RF powersupply 90 started applying the RF power, the variable DC power supply 50started applying a DC voltage at the set value of −900V to the upperelectrode 34 without gradual increase (experiment B). As a result, theratio of devices on a wafer not damaged by plasma was almost 100% inboth of the experiments A and B, i.e., the effect concerning waferdamage was not so different between the experiments A and B. Further, asregards the plasma state, stable and good plasma was generated in bothof the experiments A and B. Accordingly, it has been confirmed that thegradual increase does not affect the process characteristics, butprovide an advantage to reduce damage to the power supply.

Next, with reference to FIG. 8, an explanation will be given of anotherexample of gradual increase in the application voltage of the variableDC power supply 50. FIG. 8 is a view showing a further alternativepreferable example of an application sequence, which involves the DCvoltage of the variable DC power supply 50 and the RF powers of firstand second RF power supplies 48 and 90, along with the ON/OFF of therelay circuit 52, used in the plasma etching apparatus shown in FIG. 1.

At first, the second RF power supply 90 starts applying an RF powerlower than its set value to the susceptor 16. At the same time, thevariable DC power supply 50 starts applying a DC voltage to the upperelectrode 34 such that the application voltage is gradually increased toand then maintained at a value lower than its set value. Then, the firstRF power supply 48 starts applying an RF power at its set value to theupper electrode 34. At the same time when the first RF power supply 48starts applying the RF power, the variable DC power supply 50 startsshifting the DC voltage applied to the upper electrode 34 under controlsuch that the application voltage is gradually increased to eventuallyreach its set value. Then, after the first RF power supply 48 startsapplying the RF power, the second RF power supply 90 shifts theapplication power to its set value. The relay circuit 52 is operated inthe same manner as in the example shown in FIG. 7. Also with thissequence, the feed circuit of the variable DC power supply 50 can beless forced while damage to the wafer W is suppressed.

FIG. 9 is a view showing a further alternative preferable example of anapplication sequence, which involves the DC voltage of the variable DCpower supply 50 and the RF powers of first and second RF power supplies48 and 90, along with the ON/OFF of the relay circuit 52, used in theplasma etching apparatus shown in FIG. 1.

At first, the second RF power supply 90 starts applying an RF powerlower than its set value to the susceptor 16. At the same time, thevariable DC power supply 50 starts applying a DC voltage to the upperelectrode 34 such that the application voltage is gradually increased totrace a since curve shown in FIG. 9. Then, the first RF power supply 48starts applying an RF power at its set value to the upper electrode 34.

After the application voltage from the variable DC power supply 50reaches its set value, the second RF power supply 90 shifts theapplication power to its set value. The relay circuit 52 is operated inthe same manner as in the examples shown in FIGS. 7 and 8. Also withthis sequence, the feed circuit of the variable DC power supply 50 canbe less damaged while suppressing damage to the wafer W.

As described above, it is preferable to perform control such that thevariable DC power supply 50 causes the DC voltage applied therefrom toreach its set value, when or after the first RF power supply 48 startsapplying the RF power. Further, it is preferable to perform control suchthat the variable DC power supply 50 starts applying the DC voltage,when or after the first RF power supply 48 starts applying the RF power.

In some examples described above, the variable DC power supply 50gradually increases the voltage applied therefrom. Similarly, when theplasma etching process is ending, the variable DC power supply 50 may becontrolled to gradually decrease the voltage applied therefrom (i.e.,gradual decrease control). In this case, the timing thereof is notlimited to a specific one, but it is preferable to perform control suchthat the variable DC power supply 50 starts decreasing the voltageapplied therefrom from its set value, when or after the first and secondRF power supplies 48 and 90 stop applying the RF powers. Further, it ispreferable to perform control such that the variable DC power supply 50stop applying the voltage, when or after the first and second RF powersupplies 48 and 90 stop applying the RF powers.

The DC voltage application timing according to this embodiment may besimilarly applied to a process for sequentially etching a plurality oflayers, such as a process for first etching an SiO₂ film and thenetching an SiC or SiN film. However, such sequential etching processesinclude various processes, such as a process that requires plasma to beintermitted and a process that requires plasma to be continued.Accordingly, their application sequence is not limited to a specificone, and the sequence may be suitably designed in accordance with thecorresponding process. Where a sequential etching process is performed,the relay circuit 52 is preferably maintained in the ON-state.

Next, an explanation will be given of functions and effects obtainedwhere a DC voltage is applied from the variable DC power supply 50 tothe upper electrode 34.

The application electrode or upper electrode 34 is preferably set tohave a self bias voltage V_(dc) on the surface, at a level for obtaininga predetermined (moderate) sputtering effect onto the surface, i.e., thesurface of the electrode plate 36. In order to achieve this, theapplication voltage from the variable DC power supply 50 is preferablycontrolled to increase the absolute value of V_(dc) on the surface ofthe upper electrode 34. Where the RF power applied from the first RFpower supply 48 is low, polymers are deposited on the upper electrode34. However, since a suitable DC voltage is applied from the variable DCpower supply 50, polymers deposited on the upper electrode 34 aresputtered, thereby cleaning up the surface of the upper electrode 34.Further, an optimum quantity of polymers can be supplied onto thesemiconductor wafer W, thereby canceling the surface roughness of aphoto-resist film. Where the voltage applied from the variable DC powersupply 50 is adjusted to sputter the body of the upper electrode 34, theelectrode material can be supplied onto the surface of the semiconductorwafer W. In this case, the photo-resist film is provided with carbideformed on the surface, and is thereby reinforced. Further, the sputteredelectrode material reacts with F contained in a fluorocarbon familyprocess gas and is exhausted, thereby reducing the F ratio in plasma forthe photo-resist film to be less etched.

Particularly, where the electrode plate 36 is made of asilicon-containing material, such as silicon or SiC, sputtered siliconfrom the surface of the electrode plate 36 reacts with polymers, so thephoto-resist film is provided with SiC formed on the surface, and isthereby remarkably reinforced. In addition to this, Si is highlyreactive with F, and the effects described above are enhanced.Accordingly, a silicon-containing material is preferably used as amaterial of the electrode plate 36.

FIG. 10 is a view showing change in V_(dc) and plasma sheath thicknesswhere a DC voltage is applied to the upper electrode in the plasmaetching apparatus shown in FIG. 1. FIGS. 11A and 11B are views showingplasma states in comparison where a DC voltage is applied and where noDC voltage is applied, in the plasma etching apparatus shown in FIG. 1.

The DC voltage thus applied to the upper electrode 34 to make a deepself bias voltage V_(dc), as described above, increases the thickness ofa plasma sheath formed on the upper electrode 34, as shown in FIG. 10.As the thickness of the plasma sheath is increased, the plasma is morecompressed by that much. For example, where no DC voltage is applied tothe upper electrode 34, V_(dc) on the upper electrode side becomes,e.g., −300V. In this case, the plasma sheath has a small thickness d₀,as shown in FIG. 11A. On the other hand, where a DC voltage of −900V isapplied to the upper electrode 34, V_(dc) on the upper electrode sidebecomes −900V. In this case, since the thickness of the plasma sheath isin proportion to ¾ of the absolute value of V_(dc), the plasma sheathhas a larger thickness d₁, and the plasma is compressed by that much, asshown in FIG. 11B.

Where the thickness of the plasma sheath is thus increased to suitablycompress the plasma, the effective residence time above thesemiconductor wafer W is decreased. Further, the plasma concentratesabove the wafer W with less diffusion, thereby reducing the dissociationspace. In this case, dissociation of a fluorocarbon family process gasis suppressed for the photo-resist film to be less etched. Accordingly,the application voltage from the variable DC power supply 50 ispreferably controlled by the controller 51, such that the thickness ofthe plasma sheath on the upper electrode 34 is increased to a level forforming desired compressed plasma.

Further, when the plasma is formed, electrons are generated near theupper electrode 34. When a DC voltage is applied from the variable DCpower supply 50 to the upper electrode 34, this voltage serves toaccelerate electrons in the vertical direction within the process space(Vpp also serves to accelerate electrons). In other words, the variableDC power supply 50 can be set at a desired polarity, voltage value, andcurrent value, to radiate electrons onto the semiconductor wafer W. Theradiated electrons reform the composition of the mask or photo-resistfilm to reinforce the film.

As described above, the DC voltage applied to the upper electrode 34 canbe controlled, so as to exercise the sputtering function onto the upperelectrode 34 and the plasma compressing function, as well as the supplyfunction of supplying a large quantity of electrons generated at theupper electrode 34 to the semiconductor wafer W, as described above.This arrangement makes it possible to reinforce the photo-resist film,supply optimum polymers, and suppress dissociation of the process gas.As a consequence, the surface roughness of the photo-resist issuppressed, and the etching selectivity of an etching target layerrelative to the photo-resist film is increased. Further, the CD of anopening portion formed in the photo-resist film is prevented fromexpanding, thereby realizing pattern formation with high accuracy.Particularly, these effects are more enhanced by controlling the DCvoltage to suitably exercise the three functions described above, i.e.,the sputtering function, plasma compressing function, and electronsupply function.

It should be noted that, it depends on process conditions or the like todetermine which one of the functions described above is predominant. Thevoltage applied from the variable DC power supply 50 is preferablycontrolled by the controller 51 to exercise one or more of the functionsto effectively obtain the corresponding effects.

The DC voltage applied to the upper electrode 34 can be adjusted tocontrol the plasma potential. Where the plasma potential is decreased bythe DC voltage, etching by-products can be prevented from beingdeposited on the upper electrode 34, the deposition shield 11 forming apart of the chamber wall, the inner wall member 26, and the insulatingshield member 42.

If etching by-products are deposited on the upper electrode 34 or thedeposition shield 11 forming the chamber wall, a problem may arise inthat the process characteristics change or particles are generated.Particularly, where sequentially etching is performed on a multi-layeredfilm, since suitable etching conditions are different for the respectivefilms, a memory effect may occur in that a previous process leaves someeffect that affects a subsequent process. The amount of deposition ofetching by-products described above depends on the potential differencebetween the plasma and the upper electrode 34, chamber wall, or thelike. Accordingly, deposition of etching products can be suppressed bycontrolling the plasma potential by DC voltage application.

Further, the DC voltage applied to the upper electrode 34 can becontrolled to effectively exercise the plasma potentialcontrol-function, in addition to the sputtering function onto upperelectrode 34, plasma compressing function, and electron supply function,as described above.

The present invention is not limited to the embodiment described above,and it may be modified in various manners. For example, the embodimentdescribed above is exemplified by a plasma etching apparatus of the typethat includes an upper electrode and a lower electrode disposed to faceeach other, wherein an RF power for plasma generation is applied to theupper electrode while an RF power for ion attraction is applied to thelower electrode. However, the present invention is not limited to aplasma etching apparatus of this type. FIGS. 12 to 15 are views eachschematically showing a plasma etching apparatus of an alternative typeaccording to another embodiment of the present invention.

FIG. 12 shows an apparatus of the type that applies two powers withdifferent frequencies to the lower side. Specifically, a lower electrodeor susceptor 16 is supplied with an RF power for plasma generation witha frequency of, e.g., 60 MHz from a first RF electrode 48′, and alsosupplied with an RF power for ion attraction with a frequency of, e.g.,2 MHz from a second RF power supply 90′. In this case, the upperelectrode 134 is further connected to a variable DC power supply 101 andsupplied with a predetermined DC voltage therefrom, so as to obtain thesame effects as those in the embodiment described above.

FIG. 13 shows an apparatus of the same type as that of the apparatusshown in FIG. 12, i.e., which applies two powers with differentfrequencies to the lower side. In this type, the lower electrode orsusceptor 16 may be connected to a variable DC power supply 101 andsupplied with a predetermined DC voltage therefrom.

FIG. 14 shows an apparatus of the type that includes an upper electrode134′ grounded through a chamber 10 and a lower electrode or susceptor 16connected to an RF power supply 110 from which an RF power for plasmageneration with a frequency of, e.g., 13.56 MHz is applied. In thiscase, the lower electrode or susceptor 16 is further connected to avariable DC power supply 112 and supplied with a predetermined DCvoltage therefrom, so as to obtain the same effects as those in theembodiment described above.

FIG. 15 shows an apparatus of the same type as that of the apparatusshown in FIG. 14. In this type, the upper electrode 134′ may beconnected to a variable DC power supply 114 and supplied with apredetermined DC voltage therefrom.

In the embodiment described above, the present invention is applied toplasma etching, for example. Alternatively, the present invention may beapplied to another plasma process, such as sputtering or plasma CVD.Further, the target substrate is not limited to a semiconductor wafer,and it may be another substrate, such as a glass substrate used for anLCD.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A plasma processing apparatus comprising: a process containerconfigured to accommodate a target substrate and to be vacuum-exhausted;a first electrode and a second electrode disposed opposite each otherwithin the process container; a process gas supply unit configured tosupply a process gas into the process container; an RF power supplyconfigured to apply an RF power to the first electrode or secondelectrode to generate plasma of the process gas; a DC power supplyconfigured to apply a DC voltage to the first electrode or secondelectrode; and a control section configured to control the RF powersupply and the DC power supply, wherein the control section performscontrol such that the DC power supply causes the DC voltage appliedtherefrom to reach a voltage set value, when or after the RF powersupply starts applying the RF power.
 2. The plasma processing apparatusaccording to claim 1, wherein the control section performs control suchthat the DC power supply starts applying the DC voltage, when or afterthe RF power supply starts applying the RF power.
 3. The plasmaprocessing apparatus according to claim 1, wherein the control sectionperforms control such that the DC power supply starts decreasing the DCvoltage applied therefrom from the voltage set value, when or before theRF power supply stops applying the RF power.
 4. The plasma processingapparatus according to claim 3, wherein the control section performscontrol such that the DC power supply gradually decreases a voltage,current, or power applied therefrom.
 5. The plasma processing apparatusaccording to claim 1, wherein the control section performs control suchthat the DC power supply stops applying the DC voltage, when or beforethe RF power supply stops applying the RF power.
 6. The plasmaprocessing apparatus according to claim 1, wherein the first electrodeis an upper electrode, the second electrode is a lower electrodeconfigured to place the target substrate thereon, and the RF powersupply is configured to apply the RF power to the first electrode. 7.The plasma processing apparatus according to claim 6, wherein the DCpower supply is configured to apply the DC voltage to the firstelectrode.
 8. The plasma processing apparatus according to claim 1,wherein the control section performs control such that the DC powersupply gradually increases a voltage, current, or power appliedtherefrom.
 9. The plasma processing apparatus according to claim 8,wherein the control section performs control such that the DC powersupply gradually increases the voltage, current, or power appliedtherefrom, and the DC power supply holds the DC voltage when thevoltage, current, or power applied therefrom exceeds a predeterminedvalue.
 10. A plasma processing apparatus comprising: a process containerconfigured to accommodate a target substrate and to be vacuum-exhausted;a first electrode disposed within the process container and configuredto serve as an upper electrode; a second electrode disposed opposite thefirst electrode within the process container and configured to serve asa lower electrode to place the target substrate thereon; a process gassupply unit configured to supply a process gas into the processcontainer; a first RF power supply configured to apply a first RF powerto the first electrode to generate plasma of the process gas; a secondRF power supply configured to apply a second RF power to the secondelectrode to attract ions toward the target substrate; a DC power supplyconfigured to apply a DC voltage to the first electrode; and a controlsection configured to control the first and second RF power supplies andthe DC power supply, wherein the control section performs control suchthat the DC power supply causes the DC voltage applied therefrom toreach a voltage set value, when or after the first RF power supplystarts applying the first RF power.
 11. The plasma processing apparatusaccording to claim 10, wherein the control section performs control suchthat the DC power supply starts applying the DC voltage, when or afterthe first RF power supply starts applying the first RF power.
 12. Theplasma processing apparatus according to claim 10, wherein the controlsection performs control such that the second RF power supply firststarts applying the second RF power at a power value lower than a secondpower set value, then the first RF power supply starts applying thefirst RF power, then the DC power supply causes the DC voltage appliedtherefrom to reach the voltage set value, and then the second RF powersupply causes the second RF power applied therefrom to reach the secondpower set value.
 13. The plasma processing apparatus according to claim10, wherein the control section performs control such that the DC powersupply starts decreasing the DC voltage applied therefrom from thevoltage set value, when or before at least one of the first and secondRF power supplies stops applying the RF power.
 14. The plasma processingapparatus according to claim 13, wherein the control section performscontrol such that the DC power supply gradually decreases a voltage,current, or power applied therefrom.
 15. The plasma processing apparatusaccording to claim 10, wherein the control section performs control suchthat the DC power supply stops applying the DC voltage, when or beforeat least one of the first and second RF power supplies stops applyingthe RF power.
 16. The plasma processing apparatus according to claim 10,wherein the control section performs control such that the DC powersupply gradually increases a voltage, current, or power appliedtherefrom.
 17. The plasma processing apparatus according to claim 16,wherein the control section performs control such that the DC powersupply gradually increases the voltage, current, or power appliedtherefrom, and the DC power supply holds the DC voltage when thevoltage, current, or power applied therefrom exceeds a predeterminedvalue.
 18. A plasma processing method for performing a plasma process ona target substrate in a plasma processing apparatus, the plasmaprocessing apparatus comprising a process container configured toaccommodate a target substrate and to be vacuum-exhausted, a firstelectrode and a second electrode disposed opposite each other within theprocess container, a process gas supply unit configured to supply aprocess gas into the process container, an RF power supply configured toapply an RF power to the first electrode or second electrode to generateplasma of the process gas, and a DC power supply configured to apply aDC voltage to the first electrode or second electrode, and the plasmaprocessing method comprising: performing control such that the DC powersupply causes the DC voltage applied therefrom to reach a voltage setvalue, when or after the RF power supply starts applying the RF power.19. The plasma processing apparatus according to claim 18, comprisingperforming control such that the DC power supply starts applying the DCvoltage, when or after the RF power supply starts applying the RF power.20. The plasma processing apparatus according to claim 18, comprisingperforming control such that the DC power supply starts decreasing theDC voltage applied therefrom from the voltage set value, when or beforethe RF power supply stops applying the RF power.
 21. The plasmaprocessing apparatus according to claim 20, comprising performingcontrol such that the DC power supply gradually decreases a voltage,current, or power applied therefrom.
 22. The plasma processing apparatusaccording to claim 18, comprising performing control such that the DCpower supply stops applying the DC voltage, when or before the RF powersupply stops applying the RF power.
 23. The plasma processing apparatusaccording to claim 18, comprising performing control such that the DCpower supply gradually increases a voltage, current, or power appliedtherefrom.
 24. The plasma processing apparatus according to claim 23,comprising performing control such that the DC power supply graduallyincreases the voltage, current, or power applied therefrom, and the DCpower supply holds the DC voltage when the voltage, current, or powerapplied therefrom exceeds a predetermined value.
 25. A plasma processingmethod for performing a plasma process on a target substrate in a plasmaprocessing apparatus, the plasma processing apparatus comprising aprocess container configured to accommodate a target substrate and to bevacuum-exhausted, a first electrode disposed within the processcontainer and configured to serve as an upper electrode, a secondelectrode disposed opposite the first electrode within the processcontainer and configured to serve as a lower electrode to place thetarget substrate thereon, a process gas supply unit configured to supplya process gas into the process container, a first RF power supplyconfigured to apply a first RF power to the first electrode to generateplasma of the process gas, a second RF power supply configured to applya second RF power to the second electrode to attract ions toward thetarget substrate, and a DC power supply configured to apply a DC voltageto the first electrode, the plasma processing method comprising:performing control such that the DC power supply causes the DC voltageapplied therefrom to reach a voltage set value, when or after the firstRF power supply starts applying the first RF power.
 26. The plasmaprocessing method according to claim 25, comprising performing controlsuch that the DC power supply starts applying the DC voltage, when orafter the first RF power supply starts applying the first RF power. 27.The plasma processing method according to claim 25, comprisingperforming control such that the second RF power supply first startsapplying the second RF power at a power value lower than a second powerset value, then the first RF power supply starts applying the first RFpower, then the DC power supply causes the DC voltage applied therefromto reach the voltage set value, and then the second RF power supplycauses the second RF power applied therefrom to reach the second powerset value.
 28. The plasma processing method according to claim 25,comprising performing control such that the DC power supply startsdecreasing the DC voltage applied therefrom from the voltage set value,when or before at least one of the first and second RF power suppliesstops applying the RF power.
 29. The plasma processing method accordingto claim 28, comprising performing control such that the DC power supplygradually decreases a voltage, current, or power applied therefrom. 30.The plasma processing method according to claim 25, comprisingperforming control such that the DC power supply stops applying the DCvoltage, when or before at least one of the first and second RF powersupplies stops applying the RF power.
 31. The plasma processing methodaccording to claim 25, comprising performing control such that the DCpower supply gradually increases a voltage, current, or power appliedtherefrom.
 32. The plasma processing method according to claim 31,comprising performing control such that the DC power supply graduallyincreases the voltage, current, or power applied therefrom, and the DCpower supply holds the DC voltage when the voltage, current, or powerapplied therefrom exceeds a predetermined value.